Cell membranes Flashcards
(26 cards)
What is the thickness of cell membranes?
3-7nm
What does amphiphilic mean?
contains both hydrophilic and hydrophobic groups
What 2 structures do phospholipids form in an aqueous environment?
micelles or liposomes
What is the net charge of hydrophilic groups and what do they contains?
net anionic or neutral, contain anionic and cationic groups
What is cholesterol made up of?
polar head (-OH), rigid planar ring structure middle, non polar tail (hydrocarbon chain)
What does cholesterol do in the lipid bilayer?
lacks in the bilayer between the lipid chains. especially in unsaturated, and decreases the permeability, modulates membrane stiffness, affect cytoskeleton interactions
Explain the asymmetry of the membrane
neutral phospholipids on EC side, negative phospholipids on IC side (net negative charge), glycolipids on EC side (hydrophobic tail, hydrophilic sugar head)
Explain the term “Flip-Flop”
phospholipids switch sides in the bilayer
Why is “Flip-Flop” difficult?
difficult as hydrophilic head has to pass through hydrophobic core
Explain “Lateral” movement on phospholipids
phospholipids switch places on same side of bilyaer
Why is “Lateral” movement easy?
no energy barrier to overcome
What do transmembrane proteins do to the lipid bilayer?
disrupt lipid packing and fluidity
What conformation do transmembrane proteins predominantly have?
alpha-helical conformation with hydrophobic side chains facing hydrophobic core of membrane
How does the actin skeleton aid the membrane?
segregates it to allow different parts of membrane to have different specific functions
Define facilitated diffusion
movement of hydrophilic molecules down concentration gradient through protein pores, which are water filled filled channels that may be gated
Why does protein:lipid ratio vary and give examples
varies due to properties required by cell/organelle as more protein increase fluidity,
e.g. myelin sheath 20% protein, 80% lipid as insulator mitochondrial inner membrane 75% protein, 25% lipid as ETC & H+ channels for ATP production
Name 2 coupled transporters
symporters and antiporters
Describe symporters and give example
molecule is co-transported with another molecule in same direction as it diffuses in e.g. sugars/A.A with Na+
Describe antiporters
molecule co-transported with another molecule but moves in opposite direction
What maintains the ionic gradient?
Na+/K+ pump
Why does the Na+/K+ pump have an opposing osmotic gradient?
1) high conc. of negative charge inside cell, due to fixed anions and accompanying cations, means H2O is drawn into cell down osmotic gradient
2) high conc. of Na+ and Cl- in EC space mean osmotic gradient in opposite direction
How does the Na+/K+ pump maintain osmotic balance?
exports Na+ as it tends to diffuse into cell, so gradient maintained
What are the 2 polypeptide chains and their functions in the Na+/K+ pump?
alpha chain - spans membrane 10 times to form hydrophilic pore
beta chain - acts as controller
Name 3 bulk transport mechanisms
pinocytosis, exocytosis, phagocytosis
